In conventional magnetic recording, thermal instabilities of the stored magnetization in the recording media can cause loss of recorded data. To avoid this, media with high magneto-crystalline anisotropy (Ku) are required. However, increasing Ku also increases the coercivity of the media, which can exceed the write field capability of the write head. Since it is known that the coercivity of the magnetic material of the recording layer is temperature dependent, one proposed solution to the thermal stability problem is heat-assisted magnetic recording (HAMR), wherein high-Ku magnetic recording material is heated locally during writing to lower the coercivity enough for writing to occur, but where the coercivity/anisotropy is high enough for thermal stability of the recorded bits at the ambient temperature of the disk drive (i.e., the normal operating or “room” temperature of approximately 15-30° C.). In some proposed HAMR systems, the magnetic recording material is heated to near or above its Curie temperature. The recorded data is then read back at ambient temperature by a conventional magnetoresistive read head, i.e., a giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR) based read head. HAMR disk drives have been proposed for both conventional continuous media, wherein the magnetic recording material is a continuous layer on the disk, and for bit-patterned media (BPM), wherein the magnetic recording material is patterned into discrete data islands or “bits”.
One type of proposed HAMR disk drive uses a laser source and an optical waveguide coupled to a near-field transducer (NFT) for heating the recording material on the disk. A “near-field” transducer is an optical device with subwavelength features that is used to concentrate the light delivered by the waveguide into spot smaller than the diffraction limit and at distance smaller than the wavelength of light. In a HAMR head, the NFT is typically located at the air-bearing surface (ABS) of the slider that also supports the read/write head and rides or “files” above the disk surface while creating the sub-diffraction-limited optical spot on the disk.
In some HAMR head designs, the write head includes a write pole with a lip at the ABS. The write pole lip is located at the ABS close to the NFT. The core of the optical waveguide has an end face that abuts the NFT so that light can be transmitted to the NFT. Because of the close proximity of the write pole lip to the NFT, the waveguide core end face may also abut the write pole lip. This may result in diffusion between the materials of the waveguide core and the magnetic materials of the write pole lip, which can degrade the performance of both the write pole and the waveguide.
What is needed is a HAMR head that prevents diffusion of materials between the waveguide core and the write pole lip.